1. Field of the Invention
The present invention relates to digital data and word processing systems and more particularly to terminals employed therein.
2. Description of the Prior Art One of the most common varieties of prior-art terminal is the "dumb" terminal. A "dumb" terminal is so called because it performs no local processing of data beyond what is required to receive the data in the terminal and provide it to a digital computer or to receive the data from the digital computer and display it on the terminal screen. Communication between the "dumb" terminal and the digital computer is by means of protocols. Different protocols specify the data transferred between the digital computer and the terminal, permit the digital computer to control the operation of the terminal, and indicate the state of the terminal to the digital computer. A common class, of "dumb" terminals is made up of ANSI (American National Standards Institute) standard terminals which are controlled by means of protocols compatible with the ANSI X3.4, X3.41, and X3.64 standards.
As microprocessors, display controllers, and memory have dropped in cost and grown in speed and power, the "dumb" terminals have become "smarter". An example of such a "smart" "dumb" terminal is the IBM 3163. This and similar ANSI standard terminals now have sufficient display memory to hold more than one terminal screen's worth of data. In such terminals, the display memory is divided into pages and a user of the terminal can specify which page of display memory is to be displayed. The 3163 and others of these terminals also permit the terminal screen to be divided into viewports. A viewport is a "window" onto a page, and consequently, a terminal with viewports can display data from more than one page simultaneously.
Other areas where "dumb" terminals have grown smarter include the capability of transferring data not only between the terminal and the computer, but also between the computer and an auxiliary device connected to the terminal and the capability of displaying more than one character font. In all of these areas, the prior art has left certain problems unsolved. These problems are addressed in the improved terminal of the present invention.